Traveling wave amplifier device



Sept- 29, 1958 R. s. BAILEY 2,654,oo4

TRAVELING WAVE AMPLIFIER DEVICE Filed Aug. 14, 1947 w 2 Sheets-Sheet l '1 FIGZ 'V V V1 JNVENTOR. ROBERT s. BAILEY Flcs. 5 W

ATTO/M/EY Sept- 29, 1953 R. s. BAILEY 2,654,oo4

TRAVELING WAVE AMPLIFIER DEVICE Filed Aug. 14, 1947 2 Sheets-Sheet 2 40 2 S7 38 ae 4| lab 46 44 PLANE OF SYMMETRY INVENT OR.

ROBERT S. BAILEY BY w u A TTORNEY Patented Sept. 29, 1953 TRAVELING WAVE ARIPLIFIER DEVICE Robert S. Bailey, New York, N. Y., assi'gnor to International Standard Electric Corporation, New York, N. Y., a corporation of Delaware Application August 14, 1947, Serial No. 768,577

9 Claims. 1'

This invention relates to Wave energy amplifiers and more particularly to amplifiers of the high frequency traveling Wave type.

A principal object of the invention is to provide. a novel form of electromagnetic wave energy' amplifier employing the interaction between free electrons and a traveling wave.

Another object is to provide a more efficient amplifier of the traveling wave type.

A further object is to provide a Wave energy amplifier employing a. wave guide and meansfor producing an electron stream transversely of the wave guide for correlating the phases of the traveling Waves at various points along the guide, With the electron emission, so that a high energy transfer is supplied to the traveling Waves by the emitted electrons.

A feature of the invention relates to a traveling Wave amplifier employing a main wave guide section and an. auxi'liary wave guidesection both of which have a common wave energy input end and a common Wave energy outputend, the auxiliary section being proportioned so as to produce a predetermined time. delay in the auxiliary section, the two sections merging into a common section which has means to produce therein electron emission under joint control of the Waves from both sections in such a way as to achieve a high percentage of energy transfer from the electrons to the traveling wave.

Another feature relates to a traveli'ng wave amplifier employing a main. wave guide section with an auxiliary or shunt wave guide section, both of said sections having common input and common output ends with the output end having means to develop a stream of electrons therein and correlated with the phase of the electrical vector of the traveling wave so as to impart thereto a high energy transfer from the electrons.

Another feature relates to a traveling WaveI` amplifier employing a Wave guide which iscoi-led intermediate its ends and having means to inject free electrons through the respective coiled turns so as to achieve a high order of amplification of the traveling wave energy b-y interacton betweenV the electrons and the correlated phases of the traveling Wave.

Another feature relates to a traveling wave amplifier constituted of a wave guide which is divided into two WaveV guide sections by a foraminous wall and having means to produce electron streams transversely of both' sections. Both said sections' are supplied with high frequency energy from asuitable source in such a. Way that the Waves traveling through one section. are time del'ayed with respect to the Waves traveling through the other section so that the phase of the electrical vectors of the Waves along the length of the sections is in proper relation to provide the maximum energy transfer between the electrons and the traveling wave.

Another feature relates to an arrangement vfor amplifying high frequency traveling Waves comprising a Wave guide having input and output ends With the intervening length, of the wave guide coil'ed to a substantially planar spiral n coniunction. With an electron emitting cathode which. is mounted symmetrically at the. center of the spiral and with a pair of electroncollector electrodes mounted outside the spiral but in alignment with the cathode. Located between the cathode and the spral are electron controI electrodes which are alternately energized to cause the electrons to travel transversely, first-through the sections of the coil on'one side of 'the cathode, and then through the sections of thecoil onV the oppositer side of the cathode, for the purpose of transferring a maximum amount of energy from the'electrons to the high frequency Waves travelling through the guide.

Afurther feature relates to the novel organization, and' arrangem-entof parts, which cooperate to Vprovide an improved high frequency wave energy amplifier of the traveling wave'typer Other features and advantages will vappear from the ensuing descriptions and the appended cl'aims.

In the drawing which shows, by way of example, certain preferred embodimen-ts, Pig. 1 is a-generalized view of a traveling'wave ampl'ifier of known construction employi-ng a Wave guide section used in explaining the invention.

Fig. 2 is a graph of the electric vector of the traveling Wave in the amplifier of Fig. 1.

Fig. 3 is a perspective view of an amplifier or a wave repeater according tothe invention.

Fig. 4' is a side view of a modification of the arrangement of V`Fig'. 3.

Fig. 5 is a top plan view of-Fig.*-l. Figs. 6, `7 and 8 represent respective further I modifieations of the inven'tion.

Figs. 9a and 9b are diagrammatic views Vexplanatory of an amplifier or repeater'according to the mvention empl'oyng a rectangul'ar wave gui'deusing the TE,2. mode of transmission.

Fig. 10 is a diagrammatic view explanatory of the operation of an amplifier according to'the invention, employing' a circular'wave guide.

Referring to Fig. 1;, there is ilustrated a conventional -rectangular Vwave guidev system comcarried by the bottom wall of is an electron emitting cathode surface IB.

strip carrying on its propagated through the section for example in Fi g. 2. upper halves of E in Fig. 2 are considered as accelerating with respect to the electrons, the negaprising an input section I0, and output section II, and an intervening amplifier section I2. It will be assumed that a high frequency wave energy is received through the input section Ifl so that the various Sections are excited in the TE0,1 mode. The sections I0, I I, are conductively isolated or insulated from the section I2 by Suitable insulators or insulator joints I3, Il, so that the section I2 is insulated from Sections and I I for direct current flow, but without disturbing the alternating current field. In accordance with known theory of traveling wave amplifiers, the section I2 should have a length which is equal to one or more wavelengths of the excitation energy which is supplied thereto from the input section |0. Merely for purposes of reference, it will be assumed that the wall I5 is the top wall of the wave guide, and therefore the electrical field will exist between this top wall and the opposite or bottom wall of the guide. Suitably mounted or the guide section I2 Preferably this cathode surface is D. C. insulated from the walls of the guide section I2, for example the bottom wall of section IZ may have a window or opening into which is insulatingly fitted a metal inner surface a suitable electron emissive coating which can be raised to emissive temperature by any well-known means. The

remaining walls of the guide section I2 can be positvely biassed by source.

any suitable D. C. potential Preferably, the length of the cathode coating I6, in the direction of the wave propagation is equal to one or more wavelengths of the excitation energy. The E vector groupings of the propagated energy are schematically represented in Fig. 1 by the line groups I'I, IB, IS, etc. The Poynting's vector 1 and 1:11 indicate the direction of propagation of h igh frequency energy through the system. The E vectorS at odd maxima, for

I9, may be considered positive,

example at I'I and for example IB, they while at the even maxima, may be considered negative.

With the wall |5 at a suitable positive D. C. potential the electrons from the emitted surface |6 will drift along the Y axis. When no high frequency or radio frequency wave energy is present in the section I2, and for values Ep of the D. C. potential applied to wall I5, at which potential it is assumed that the relativity effect does not enter, these electrons from surface I6 will absorb energy from the positive electric field and will give it up at the surface of wall I5 in the form of heat and current fiow. Under such conditions the electrons will, as is well-known, arrive at wall I5 with a velocity decelerating them. If the net effect of the traveling wave field is a deceleration of the electrons, then energy is supplied to the radio frequency field from the D. C. field, and amplification of the wave energy takes place.

For example, as-

suming that ampliflcation takes place, the magnitude of the vector in the guide can be represented by an increasing quasi-sinusoid, as shown If the positive, that s the 4 tive or lower halves of are decelerating in action. Since the negative halves are larger in amplitude than the next preceding positive halves, there occurs a net deceleration over an integral number of cycles.

From the foregoing, it will be seen that if the electrons are moving in the same coordinate system as that of the traveling wave and at the same Velocity in this system (that is if the electrons are injected at the same Velocity as the wave guide Velocity), then only those electrons which are emitted at a negative or decelerating -Spacetime position, will give up energy to the radio frequency field. However, those electrons emitted from IS at accelerating -space time positions will take less energy from the radio frequency waves under either of the following conditions:

(1) The number of electrons at these accelerating positions are fewer; or

(2) The Ep field is opposite to that which exists at a point xg/z away.

Under these conditions, the dimensions of the wave guide are not critical when the electrons move with the wave.

One of the principal difficulties of the foregoing described type of amplifier is in making sure that the electron injection from the surface I6 is effected at the speed of the traveling radio frequency wave. Various attempts have been made to achieve this result, for example by slowing down the radio frequency wave by means of a coil. This known type of expedient is not predicated mainly on either of the above-mentioned alternatives. I have found that this slowing down effect can be greatly increased by purposely arranging the system so that fewer electrons are emitted from the cathode IB at the undesired time instant. One typical arrangement for accomplishing this result is shown in Fig. 3. In this figure the amplifier section 20 of the wave guide corresponding to the section I2 of Fig. 1, is divided longitudinally into two parts by means of an open-work metal wall or grid 2|. The section 20 is preferably closed at its ends for example by glass walls, and the interior of section 20 is highly evacuated. The coupling for A. C. wave is well-known in wave guide systems. The lower wall 22 of this guide has a window or opening in which is insulatingly fltted the metal plate 23 having its inner face provided with an electron emissive coating 24 which can be raised to emitting temperature by any well-known heating means (not shown). The input section 25 of the guide communicates with a branch 26, so that the input wave energy is divided into two guide paths deslgnated respectively by the arrows a and b. The length of the branch 26 from the point of its coupling to the input section 25 and to the point of its coupling to the amplifier section 20, is designed so that at the common region where the Sections 25 and 26 couple to the amplifier Section 20, the Waves arriving over branch 26 are delayed by xg/2 with respect to the Waves arriving directly from Section 25. Thus the Section 20 may be considered as made up of two wave guides having a common foraminous dividing wall 2|, the upper portion 21 of section 20 receiving the wave propagation directly through section 25, and the lower portion 28 receiving the propagation through the branch 26. Thus in the Section 28,

- the radio frequency field of the traveling wave 2|, namcly at those points where the electric field of the traveling Waves in section 21 have a decelerating action on the electrons which emerge through the grid' 2t. On theother hand, when the electric field of the traveling Waves in section 21 are in the acceleratingzphase, the-traveling Waves in the section 28 are in a decelerating phase, thus reducing considerably the number of electrons'which emerge through the grid 2| at this region. The section 28 may be terminated by a suitable termination or preferably'its. output can by a suitable couplin-g be added to the output from the section 21. While there may besome wave amplification in the section 28, it is onlyto a slight degree as compared with the resultant Wave amplification. in section 21.

It will be understood of course that the section 2a is D. C. insulated from the input and output sections, such as Sections Hi, H (Fig. 1), without afiecting the A. C. field. lLikewiseL as described above in connection with Fig. l, theV upper wall 2'9' can be connected to a suitable positive D. C. potential with respect to. the cathode.. If the' work function of the cathode 24 is Ew, a small positive D. C. potential Epb should exist between the cathode 24 and the foraminous wall 2|., so that. during the deceleration cycles of the traveling Waves the fields of these Waves just cut ofiE the electron current at the deceleration half-cycle, represented schematically by the arrow 3G. transit time between 23. and 2| is negligible, or

if the length of section 26 is designed to take into account this transit time, the electrons from cathode 24 will emerge through the grid 2| into guide section 21 in the presence of a strong D. C. :z

accelerating field, as represented schematically vby the arrow 3-l3. But at this instant,the field in the section 21 at the region represented by arrow 3| willbe strongl'y d'ecelerating. In other words,

the field of the traveling wave in section 21 has its E vector decelerating at the same instant the 'electrons are being highly accelerated into the section 21 by the simultaneous accelerating action of the E vector in section 28. The positi've D. C. potential applied across wall 29 and' grid 2| should be such as to cause the average eIectron to give up the maximum of its energy'before it is collected by the surface 29.

There will of course be some wave amplification 'in the section 2'8 and theoretically' this ampli- 'fication may be of the order of 50%. However, in

section' 21 theoretically the maximum amplification will be nearly 99% resulting in a greatly inoreased over-allamplification efiiciency, particularl'yV when the amplified output of section 28 is added to the amplified output of section 21. In order further to increase the ampli-'fying efliciency,

the section instead of' being straight, can be coiled into a helix, asillustrated in Figs. 4 and 5,

providing the radiu-s. of this helix is not made too small. With a sufiiciently largel helix, the abovedescribed amplifying action can be obtained without disturbance of the radio frequency Waves traveling through the guide. While Figs'. 4 and 5 show the amplifying; section formed with aV single helical turn,` it will be understood that itmay be formed with. two or morehelical turns. In effect, by coil-ing the amplifyi-ng section as shownv in Fig. 4, the rectangular cathode 24 of Fig. 3. is'now of cylindrical shape. Therefore, this cylindrical cathode can be conveniently provided with a central heater (not shown). of any suitable design, so

as. to raise it. to. emitting temperature.

While.| in vFi'gs. 3v and 4 there is provided an auxiliary path or T-ju-nction 26, for obtaining the If the electron phase change of. rtg/2 (or odd'multiple thereof), other` well-known arrangements may be provided for obtaining this relative .phase d'eIay between the Waves entering the section 28, asv compared with the Waves entering the section 21, thus. allowthe T-junction to become a matched Y- iuncion.`

Referring to Fig. 6,. there is shown a further modification wherein the wave guide is split along its plancV of symmetry represented by the dot-dach line, so as to form. Y branches 32, 33. Thebranch 32 merges into an `amplifier section 34 similar to section 2a (Fig. 3) comprised of twoadjacentwave guides .35, '36, having a common foraminous boundary wall or grid 31. The wall of *section 36 which is opposite to wa1131 carries an electron emitting cathode 38 for injecting electrons into the wave guide sectionl 35 under control of grid 31 and the electric field. of the traveling wavesin guide Vsection 36. It will be understood that the cathode 38 is. suitably D. C.. insulated Vfrom the wall 31 and from the remainder' ofguide 34. It will also be understood that the amplifier section 34 is D. C. insulated from the remainder of the wave guide system Without aifecting the A.4 C. fields within the guide. As mentioned above, the upper wall of guide 34 can be suitably biassed positively with respect to the cathode 38. coupled for wave propagation Vto the section 36. but- D.. C. insulated therefrom, is an input wave guide 39. The Y branch 32 which is coupledto the section 3'5 is also coupled to a wave guide section 40- both of which are excited by'the input waves,`for ex;- ample in the TEo,1 mode, froma suitable source.

Likewise the Y branch 3.3 and the corresponding wave guide section 41 are coupled for A. C. propagation to an amplifier wave .guide section 42 similar to section 34, having two wave guide 'Sections 43, 44, with a common foraminous con'- ductive separating wall or grid 45. The Wall of section. 44 opposite. to grid 45 carries an electron emitting oathode 46 which is suitably D'. C. insulated from theguide 42 and is arranged to be raised to 'emission temperature by any suitablev means which may be the-same means that heats the cathode 38 as above described. The Sections 35, 36 can be suitahly phased with respect to veach other as. described above in connection with Fg.v 3 by properly designing the length of the Y branch 32.. Likewise the sec.- tions 43 and 44 can be properly phased by designing the appropriate length for the: section 33. The. outputs from the amplifier sections 34 'and- 46 can be appropriately combined so as to increase the over-all amplification of the system.

By correctly matching all. the wave guide j-uncti'ons in known. manner, refiection losses can be avoided. In the case of the coiled wave line embodiment of F'ig. 4, and in. the subsequent coiled embodiments to be. described, reflection losses can be minimized if theV constants. of the guides. are preserved while forming the -helices. This will. result in large. propagational velocties, but since the helix can be installed economically inrelatively small space, sufiicient. D. C. potential can be used to transfer a substantial part of the-energy from they electrons into the traveling wave. If the Velocity of the wavev propagation is too high, for example greater than the Velocity of light, the Wave guides above described should have their diameters or transverse dimensions correspondingly changed to lower the propagational Velocity, and by also using appropriate match-ing. means at. each end.

Referring. to Fig.. 7,. there is shown a further modiflcation wherein wave ampliflcatio'n is obtained by employing for example a circular wave guide 41 which is rolled up into a spiral, so that all the turns are in substantially the same plane and preferably with the walls of the adjacent turns in contact. With such an arrangement, along the fline L-L, the wall-to-wall radio frequency voltage of the guide is in phase. In 'accordance with the invention, the walls of the turns are provided with windows or openings all of which are in alignment along the line L-L. Adjacent the outer window 48 is an electron gun 49 or any other well-known means for developing a beam of high Velocity electrons which can be focussed or directed so as to move along the line L--L. If desired, a high potential anode 50 can be located adjacent the opposite window to facilitate the acceleration of the electrons in the beam. By appropriate means, for example by the grid 52 the electron beam can be blanked off at an appropriate rate by any well-known source of periodic blanking potentials. The passage of the electron beam serially through the several turns of the coiled wave guide is timed so that they pass transversely through each turn only at the instants when the E vector of the traveling wave propagated through the guide 41 has a decelerating action on the electrons emanating from the gun 49. The energy of these electrons is then transferred to the radio frequency field and the amplitude of the traveling wave in the guide is correspondingly increased.

Referring to Pig. 8, there is shown a modifica- 'tion of the traveling Wave amplifier embodiment of Fig. 7, but wherein easier control is obtainable over the proper phase relation between the traveling waves and the electron emission. In this embodiment. the wave guide 53 which may be a circular wave guide, is coiled to substan- -2 tially spiral form, as in the case of Fig. '7. Likewise, the walls of the adjacent turns of the spiral have aligned windows. Centrally mounted within the spiral is another suitable electron emitting cathode 54, and located on opposite sides of the L.

cathode 54 externally of the spiral wave guide and in alignment with the windows, are respective anodes 55, 56 which are suitably biassed positively with respect to the cathode 54. Located between the cathode and the inner turn of the spiral wave guide, are two accelerating grids 51, 58. The grids 51 and 58 are connected respectively to a radio frequency oscil'lator 59 in push-pull relation so that when one grid is bi'assed positively with respect to the cathode 54, the other grid is biassed to plate current cutoff. The oscillator 59 is adjusted to operate at the same frequency as the frequency of the waves propagated through the guide 53. By this arrangement, the electrons from cathode 54 are alternately accelerated, first in one direction 'through the coil turns towards the anode 55,

and then in the opposite direction through the coil turns towards the anode 55. The spirally formed wave guide 53 is so dimensioned, that regardless of whether the electrons are flowing to anode 55 or to anode 56, the electric field of the traveling waves within the guide are always in decelerating phase with respect to the electrons passing through the guide from the cathode 54, resulting in 'a greatly increased overall wave amplification at the output end 60 of the guide.

While in Fig. 8 the electrons from the cathode 54 are subjected to alternate or two-phase control. it will be understood that the cathode 54 may be provided with three or more grids symmetrically surrounding the cathode, and each of these grids will then be in alignment with a corresponding aligned set of windows in the spiralized wave guide. These grids can then be connected to any well-known form of polyphase radio frequency oscillator so as further to increase the over-all wave amplification at the output end of the guide.

In all of the foregoing embodiments, it will be understood that the interiors of the amplifier Sections, for example section 20 (Figs. 3 and 4), sections 34, 46 (Fig. 6), are evacuated in any suitable manner, for example these ends of these Sections may be closed-ofi by suitable glass insulators, and these Sections can be coupled to the input and output wave guides by capacitor couplings as is well-known in the wave guide art.

While in the foregoing descriptions reference has been made to the TEN mode of wave propagation, it will be understood that other modes can be employed to achieve the desired amplification. Thus there are shown schematically in Figs. 9a and 9b the distribution of the vector in a rectangular wave guide excited in the TEo.: mode. In the case of circular wave guides as represented schematically in Fig. 10, the guide may be eigcited in the 'I'E1,i mode. With this mode the E vector lines are symmetrical as illustrated in Fig. 10, in which case an electron emitting cathode, corresponding to cathode 24 (Fig. 3) can then be mounted within the guide in this plane of symmetry, without disturbance, and

i providing of course the cathode is maintained negative with respect to the guide walls. Furthermore the invention is not limited to wave guides of rectangular cross-section and therefore circular cross-section wave guides may also be employed.

While certain particular embodiments have been described, various changes and modifications may be made therein without departing from the spirit and soope of the invention.

What is claimed is:

1. Apparatus for amplifying high frequency wave energy, comprising a pair of wave guides each having an input end and an output end and the pair having a common electron permeable separating wall, means in one of said guides to emit electrons transversely thereacross through said dividing wall and thence transversely across the other wave guide, and means to introduce traveling wave energy into the input ends of said wave guides in opposite phase with respect to their action on the emitted electrons.

2. Apparatus for amplifying high frequency wave energy, comprising a pair of wave guides, means in one guide to emit electrons into the other guide, a wave guide coupled to both said wave guides on one side of said electron emitting means for applying high frequency energy thereto, a wave guide coupled to both said wave guides on the other side of said electron emitting means for extracting the amplified high frequency energy therefrom and means to delay the electric field of the wave energy in the first guide with respect to the field of the wave energy in the other guide whereby more electrons are emitted into said other guide when the electric fields in said other guide are in decelerative phase with respect to said electrons as compared with the number of electrons that are emitted into said other guide when the electric fields in said other guide are in accelerative the electrons.

3. A wave amplifier of the traveling wave type, comprising a Wave guide, means for emitting electrons interiorly of the guide and transversely thereacross, a foraminous conductive member dividing said guide into two sections, means for coupling one of said sections to a source of high frequency Wave energy, and means for coupling the other of said sections also to said source, the last-mentioned means including means to delay the wave energy excitation of one of said sections with respect to the wave energy excitation of the other of said sections so that for corresponding regions of both said sections the electric fields are of substantially opposite phase.

4. A high frequency wave amplifier of the traveling wave type, comprising a wave guide, a foraminous conductive wall dividing said wave guide into two similar wave guide sections, an electron emitting cathode carried by one of said sections for emitting electrons transversely therephase with respect to across and thence through said dividing wall and transversely across the other section, a T-junction for coupling a source of high frequency wave energy respectively to said sections, one leg of the T-junction being of greater transmission length than the other so that at corresponding regions of said two sections the electric fields of the traveling Waves are of substantially opposite phase with respect to the electrons from said cathode.

5. A traveling Wave amplifier according to claim 4 in which said sections of the traveling wave amplifier are adapted to be coupled to said source through respective Wave guides one of which delays the electric field by one-half the wave length of the traveling wave.

6. A traveling wave amplifier according to claim 4 in which said dividing wall is adapted to be biassed with respect to the cathode so that when the electric fields of the traveling Waves in the first section are in decelerative phase with respect to the electrons, the electron emission s substantially cut off from the other section.

7. A traveling wave amplifier according to claim 4 in which said wave guide is coiled to helical shape.

8. A traveling wave amplifier according to claim 4 in which said wave guide is of the rectangular type having said cathode forming one of the walls between which the electric fields are propagated, said guide being coiled to helical shape whereby said cathode assumes a substantially cylindrical formation around the interior of the coil.

9. A traveling wave amplifier comprising a pair of amplifier units, each unit consisting of a Wave guide divided into two sections by a foraminous conductive wall, each unit also having means to emit electrons transversely across both sections and through the respective foraminous wall, means to couple both of said units to a source. of high frequency energy, the last-mentioned means including a pair of linear wave guides for coupling the corresponding sections of said units to said source, and a Y-juncton wave guide having the arms of the Y respectively coupled to the other sections of said units to cause the electric fields of the wave energy in the two sections of each unit to be of substantially opposite phase.

ROBERT S. BAILEY.

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